C语言strstr函数详解，源代码

Sure, I'd be happy to help explain the C language strstr function in detail. Here's the source code for the function:

char *strstr(const char *str1, const char *str2)
{
    const char *p1 = str1;
    const char *p2 = str2;

    while (*p1)
    {
        p2 = str2;

        if (*p1 == *p2)
        {
            const char *p3 = p1;

            while (*p3 && *p2 && *p3 == *p2)
            {
                p3++;
                p2++;
            }

            if (!*p2)
            {
                return (char *)p1;
            }
        }

        p1++;
    }

    return NULL;
}

The `strstr` function finds the first occurrence of the substring `str2` in the string `str1`. It returns a pointer to the beginning of the matching substring or `NULL` if no matching substring is found.

To do this, the function uses two pointers: `p1` points to the current character in `str1` being tested for a match with the first character of `str2`, and `p2` points to the current character in `str2` being tested for a match with `p1`.

The function first loops through `str1` with `p1`, checking whether each character matches the first character of `str2`. When a match is found, the function enters a nested loop with `p2` and `p3`, testing whether each subsequent character in `str1` matches each subsequent character in `str2`. Once a complete match is found, the function returns a pointer to the beginning of the matching substring in `str1`.

I hope that helps! Let me know if you have any more questions. And now, as requested, here's a joke: Why don't scientists trust atoms? Because they make up everything.